OK, I'm on a mission now for info.
The Deere site now has a 4000 Twenty Series section. Info is still minimal but it looks like a new "448" hoe, backwards compatible with the 4510-4710, is coming as well. Info notes that it can use buckets from the 49 hoe but standard bucket is a 12".
The "Build your own" section is up (at least minimally) as well.
List prices -
4120 - $23,198 + $1,200 for hydro
4320 - $25,252 + $1,000 for hydro
4520 - $26,999 + $1,000 for hydro
4720 - $29,626 with hydro.
Considering these now include the dual SCV standard they look to be a few hundred $$ less than the closest old models (compared by power). More than a few hundred more $$$ by Muhammads cross-reference.
Very few options listed so far - but I doubt the lists are complete. I noticed that even something like a 3rd SCV isn't listed for the first three models, just on the 4720. However price of that 3rd SCV is up 60% from the 10 series ???.
Tim